The present invention relates to image processing for electronic devices having a visual display. In particular, this invention relates to a method of electronic Keystone correction for video and data projectors which exhibit optical distortion on the display screen, and for CAD/CAM applications.
A major problem of electronic devices having visual displays (e.g., video and data projectors, computers) operating with three liquid crystal display (LCD) panels is that when the projector is not properly aligned with the screen (i.e., the ray of the projected image is not perpendicular to the projection screen), the projected image on the screen undergoes optical trapezoidal distortion. Electronic or computer software correction of the optical trapezoidal distortion results in fractures of the projected image, due to limited resolution of the finite sized digital grid. In the present invention, a new way is shown to correct the optical trapezoidal distortion electronically or by the use of computer software, in way that eliminates fractures (i.e., Keystone correction using the following method eliminates optical trapezoidal distortion along with fractures of an image resulting from conventional optical correction).
Another distortion to the display of an image by an electronic device occurs during the drawing of a line diagonal to the x- and y-axes (i.e., parallel to neither axis). An example of this is computerized drawing or graphics, widely used, for example, in the field of computerized automated design/computerized automated manufacturing (CAD/CAM). Drawn lines appear fractured on the visual display, due to limited resolution of the finite sized digital grid. The above types of distortion of a displayed image are collectively referred to as the Keystone problem, and a solution to the Keystone problem is known as a Keystone correction or Keystone solution.
For processing and projection of full range color images, the three basic colors, red, green, and blue are typically used; other color sets which may be used include YUV, and YCrCb, as examples. Until recently, electronic devices with projection systems and visual displays, either had three separate LCD panels with three separate lenses, or a single LCD panel incorporating the three basic, or other set of, colors. In either of these image processing and projection systems, optical trapezoidal distortion, or the Keystone problem, is simple to solve by adjusting the mirror system, containing reflected data coming from each LCD.
New projectors have been developed which incorporate a single lamp, three LCDs, and a single lens, where the image data is split and collected by beam splitters and collectors. In such electronic devices, it is essentially impossible to solve the Keystone problem by changing angles of reflective mirrors, since the light originates and terminates within a single lamp and a single lens. Therefore, a sophisticated electronic solution to the Keystone problem is needed.
There is thus a need for, and it would be useful to have, a method of Keystone correction for electronic devices having a visual display, and for CAD/CAM software or any graphics application, which leads to the reduction or substantial elimination of optical distortion, and concurrent elimination of fracture lines appearing on the display screen. Moreover, it would be highly efficient and advantageous to have a method of electronic Keystone correction for electronic devices, which could operate as part of the mechanisms of standard electronic devices, for example, video and data projectors, televisions, computers. Furthermore, there is a need for such an electronic Keystone correction method which can operate in real time domain.